Building an existing Makefile application for OpenWRT

I'm trying to create a package for OpenWRT from a simple Makefile project.
My problem is that somehow the the CC and other toolchain variables are not propagated. My Makefile is smart enough to use them.

I tried to manually set those variables like

define Build/Configure
    CC:=$(TARGET_CC)
    echo ${CC}
endef

but then I get something like this:
[...]

CC:=aarch64-openwrt-linux-musl-gcc
bash: line 1: CC:=aarch64-openwrt-linux-musl-gcc: command not found

[...]

I also came across this article, but it seems has no effect.

It seem that the build system is trying to set those variables, but since I have no configure script, it fails. (I also tried creating a fake configure script without success). I get this:

cd /home/lev/openwrt/build_dir/target-aarch64_cortex-a72_musl/some_package-4.3.0/./;
if [ -x ./configure ]; then [...]
CC=“aarch64-openwrt-linux-musl-gcc”
GCC=“aarch64-openwrt-linux-musl-gcc”
[...]  fi; )

I need the above variables set.

This is how my Makefile looks like:

include $(TOPDIR)/rules.mk
PKG_NAME:=some_package
PKG_VERSION:=4.3.0
PKG_RELEASE:=$(AUTORELEASE)
PKG_SOURCE:=v$(PKG_VERSION).tar.gz
PKG_SOURCE_URL:=https://github.com/some_package
PKG_HASH:=7dceddba2981c3fccdc1fcda7d782dc0b4566462defda9612c48ee3ba7ac096e
PKG_BUILD_DIR:=$(BUILD_DIR)/some_package-$(PKG_VERSION)
SDK_DIR:=/home/lev/Downloads/some_sdk-4.3.0
MAKE_VARS = \
      CC=$(TARGET_CC)
include $(INCLUDE_DIR)/package.mk
define Package/some_package
    SECTION:=iot
    CATEGORY:=IoT
    TITLE:=x
    URL:=x
    MENU:=1
    DEPENDS:=+libc +libm +libstdc++
endef
define Build/Prepare
    mkdir -p $(PKG_BUILD_DIR)
    echo “Copying files....”
    $(CP) -r ${SDK_DIR}/* $(PKG_BUILD_DIR)
endef
#define Build/Configure
#    CC:=$(TARGET_CC)
#    echo ${CC}
#endef
define Build/Compile
    echo ${CC}
    ${MAKE} -C ${PKG_BUILD_DIR}/some/long/path/some_package -f Makefile_openwrt
endef
define Package/some_package/install
    $(INSTALL_DIR) $(1)/usr/bin
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/some/even/longer/path/for/the/exe $(1)/usr/bin/
endef
$(eval $(call BuildPackage,some_package))

Any help appreciated.